1. Field of the Invention
This invention relates to the venting of waste tanks or other such systems in which noxious odors and gases are vented to the atmosphere, and more particular to the positive ventilation of vehicle waste tanks in which human waste is maintained for some period of time.
2. General Background
Sealed tanks in general frequently need to be vented to allow for expansion and the free flow of the materials being delivered from the tank. These vents are most often direct to atmosphere. However, in some cases vent exhaust fans are used to improve the discharge rate when the tank's discharge valves are open or when the tank is otherwise vented. The present invention is well suited for such applications. The present invention allows for the direct discharge to atmosphere when no vacuum can be achieved on the tank. However, when the tank is closed a vacuum can be achieve by the exhaust fan. In which case, with the addition of an auxiliary exhaust port exiting the fan chamber, the fan chamber becomes a mixing chamber for mixing vapors from the tank through the intake port with fresh air taken in through the primary exhaust port. Therefore, it has been discovered that ratios in excess of five parts fresh air to one part tank vapor can be achieved. The volumetric discharge rate through the auxiliary exhaust port is significantly smaller than could be achieve by natural ventilation methods. Therefore dilution of the tank vapors is achieve not only through fresh air to vapor mixture ratio but also by dilution over a much longer period of time. It has also been discovered that an even further dilution can be achieve by piping the auxiliary exhaust port back into the primary exhaust duct thereby recirculating the mixture.
One example of where the present invention has been found very useful is on recreation vehicles and portable toilets. The invention is used in conjunction with recreational vehicles such as boats and campers where the toilet facility generally comprises a relatively small room within which is housed the toilet and bath facility. The sewage collected from the toilet is kept within a holding tank mounted below the toilet facility. From time to time the holding tank must be dumped by draining its contents into a sewer system.
When the recreational vehicle, boat etc. is exposed to heat such as during the summer months, when they are the most active, the sewage within the holding tank becomes bacteriologically active resulting in noxious odors. Chemicals are usually added to help naturalize the odor and speed the biodegradation of toilet paper. Until recently formaldehyde, a hazardous chemical, was the chemical of choice to control such odor.
Usually, the holding tanks are vented to atmosphere, by way of a vent pipe, to allow for the dissipation of gases and odor. However, a vent pipe alone does not solve the problem of noxious odor, chemically treated or not, from backing up into the room where the toilet is housed. Whenever, the toilet gate valved is opened to allow waste to enter the holding tank the noxious chemically laden odors rise, permeating entire area. In addition these odors are constantly being emitted into the air around the vehicle.
A primary object of the prior art, in most cases, is to provide a ventilation system for portable or vehicle toilets whereby any noxious odors or gases are positively expelled. To do this, various methods of ventilation have been employed, such as vent fans mounted in or over the tank vent pipe and forced draft suction created by the movement of air passing over vent pipes or ducts.
The need for positive ventilation, in vehicles or portable toilets, sometimes referred to as black water tanks, has been acknowledged in such U.S. Patents as U.S. Pat. No. 4,042,981 which utilizes a vent fan blowing across a tank vent tube, U.S. Pat. No. 949,212 which utilizes a fan, mounted inside the vent tube and rotated by a wind turbine, to remove odors and U.S. Pat. No. 4,922,557 which utilizes solar panels to power a fan located on top of the exhaust vent. Each of the above patents attempt to achieve positive ventilation of the toilet tank and/or the water closet in which it is located.
Through toilet cleaning of the waste tank is an unpleasant task at best but is particularly obnoxious if the tank is not continuously being positively vented. This operation is accomplished when the toilet gate valve is opened, allowing access to the tank, where a water hose with a nozzle attachment is used to swab the tank during the dumping operation. Without positive ventilation at all times, toilet odor becomes offensive inside the vehicle or portable toilet. Recreational vehicle users have come to rely on chemicals to reduce the holding tank odor to reasonable levels and therefore, expect and accept such chemical odors. Newer chemicals, considered to be more biodegradable and non-hazardous, are now being substituted for the formaldehyde formula. However, we can never be sure if they too will not have some side effects on humans or our environment.
The prior art, fails to address the critical problem of what should be done with the odor once it is removed from the vehicle. Simply exhausting such odors into the surrounding air may be sufficient when the vehicle is moving. However, such practice is clearly unacceptable when the vehicle is parked for several days. Constant atmosphere emission in an area with little wind circulation can be just as unpleasant as being near the toilet. Recreational vehicles are seldom parked alone, thus, such odors are combined when several vehicles congregate. Anyone attempting to enjoy the great outdoors, when surrounded by vehicles exhausting noxious and/or chemical odors, may find the air to be very unpleasant.
Therefore, one object of the present invention is to provide a means of positively exhausting toilet odor in a manner which provides for the dilution of the waste tank odor.
A further object of the present invention is to provide a continuous operating toilet exhaust fan that does not interfere with television or stereo equipment.
It is a further object of the present invention to reduce the dependence on chemicals used in vehicle holding tanks with better distribution. Thus, the amount of chemicals required to reduce toilet odor can be reduced.
Still a further object of the present invention is to provide a positive ventilation system for exhausting vapors from sealed tanks in a manner which dilutes such vapors as much as possible before emitting such vapors into the atmosphere.